Which Testing Framework Should I Use?

Honestly, it doesn’t really matter. Jest is built on top of Jasmine and Vitest is a drop-in replacement for Jest (mostly). We’re going to use Vitest during our time together, but everything we do should apply to Jest as well. If and when it doesn’t, I’ll make it a point to call it out.

But, if you really wanted to know my heuristic, here it is:

• Jest is maintained by Facebook, who coincidentally maintain React. And, it comes built-in with Create React App. So, I’ll usually just use Jest if it’s already there because I am very lazy.
• Vitest is optimized to work with Vite (an alternative to Webpack). By default, Vue and Svelte applications use Vite. React applications can use Vite as well and there is even a boilerplate (e.g. npm create vite@latest my-app --template react, which works suspiciously similar to create-react-app. I chose it for this course it’s the most broadly applicable.
• Angular uses Jasmine by default. But, like I said, Jest is based on Jasmine and Vitest is a drop-in replacement for Jest.

Speed and Performance

Jest

Jest has been around the block. Built by Facebook, it’s perfect for testing React apps (and others!) and has a reputation for giving you everything you need out of the box—mocking, snapshots, you name it. But here’s the thing. Jest can sometimes feel a little… slow. Not glacial slow, but slow enough that you’re going to start wondering if your code has some existential crisis every time the test suite runs. It uses the Node runtime exclusively, which is great for stability, but can limit its execution speed compared to other approaches.

Vitest

Vitest? Built on Vite—yes, that lightning-fast bundler—and this speed advantage becomes one of its calling cards. Vitest leans into the Vite ecosystem and uses ESM (EcmaScript Modules), which allows for crazy fast start times and lightning-fast testing, especially in development mode. The ability to run tests directly in a browser without additional setup brings a major boost in speed for frontend-heavy projects which, let’s be real, is 90% of what we’re doing these days, right?

Setup and Learning Curve

Jest

Setting up Jest isn’t the worst thing you’ll face as an engineer—ever try to configure Webpack from scratch in like 2018? It does come batteries included, so 90% of the time, you install it, and boom—you’ve got a functional test suite.

But—and it’s a big but—the Jest API array of features can sometimes tip over into the “whoa, okay, let me get back to you in a week” territory. If you’re tackling newer features like parallel testing or even type hints sometimes, suddenly you’re knee-deep in documentation.

Vitest

Vitest, by comparison, is a smoother onboarding if you’re already in the Vite ecosystem. The same way Jest “just works” for React, Vitest “just works” for Vite-powered projects. Configuration’s simple, the syntax is almost identical to Jest (so anyone making the switch won’t feel like they’ve been dropped into a foreign country), and it’s very lightweight in terms of setup.

Set up Vite already? Then you’re like 90% of the way there. It’s like Vitest sidled up to you at the coffee shop and quietly said: “Hey… no big deal, but… wanna test this?”

Mocking and Stubbing

Jest

Now, if there’s one thing where Jest shines, it’s the built-in mocking. Some devs will live and die by Jest’s powerful ability to mock modules, functions, objects—you name it. Jest makes it dead simple, and you don’t usually need third-party libraries to handle the heavy lifting.

const myModule = require('./myModule');
jest.mock('./myModule');

And boom, you’ve got a mock. It’s a favorite feature for many since mocking often makes the difference between a 3-minute test run and an afternoon fighting with dependencies.

Vitest

Vitest can also mock, but it’s not quite at Jest’s level… yet. While it supports mocking modules, functions, and such, some of the more complex use cases, like auto-mocking, are still catching up. However, it does integrate with Sinon.js easily and can handle most commonly needed mocks without breaking a sweat.

import { vi } from 'vitest';
import myModule from './myModule';
vi.mock('./myModule');

See? Syntactically similar to Jest, but a little different under the hood.

TypeScript Support

Jest

Jest does work with TypeScript, but setting it up requires some legwork. You’ll have to make sure your transpiler (usually Babel or ts-jest) is configured correctly with proper transformers which, frankly, is a bit of a pain in the neck, and often the primary source of “what fresh hell did I just walk into” moments.

Vitest

The story is different for Vitest. Since Vite inherently supports ESM and TypeScript, Vitest inherits that awesomeness. No need for Babel or special transformers—just point it at your TypeScript files and go. Seriously, it feels like cheating when you see how smooth it is. No translation layer shenanigans here!

Snapshot Testing

Jest

Snapshot testing is another one of Jest’s killer features. You generate a snapshot of your UI functions or components, and Jest makes sure those snapshots don’t change unless you explicitly want them to. It’s a great fit for React or any UI you want to keep a close watch on.

expect(component.toJSON()).toMatchSnapshot();

Instant peace of mind.

Vitest

Vitest also supports snapshots. However, if you’ve built up a mountain of Jest snapshots, they aren’t directly transferable. That means switching might require a bit of work converting, and Vitest’s snapshot functionality doesn’t have the same level of maturity—for now. It gets the job done, but I wouldn’t print the victory cake about switching just for snapshots alone.

Which One Is Right for You?

At the end of the day both are great for testing your JavaScript projects. But here’s the real-world takeaway:

• Using Vite and a modern ecosystem? You’re probably going to enjoy Vitest’s faster start times, seamless TypeScript integrations, and simplicity.
• Deeply reliant on Jest’s mocking, parallelization, or snapshot APIs? Jest might still hold the crown for you, especially if it’s already baked into your tools and workflow.